Indicator



Sept. 7, 1937. M. A. MCLENAN INDICATOR Filed Oct. 26, 1934 60 OYCL E SOL/ECE n INI/E/vTo/e: MLZeJjiMULefzmm Patented Sept. 7, 1937 INDICATOR Miles "A. McLennan, Palmyra, N. J., assigner, by mesne assignments, to Radio Corporation of America, Delaware Application October 26, 1934, Serial No.

3 Claims.

to indicators, and more particularly to a device utilizing a cathode ray tube for forming an image on the screen thereof, the position of the image along the arc of a circle being rendered indicative of some relationship between two existing conditions. i

If, for example, two sources of alternating current are to be applied, one to the deflecting circuits of the cathode ray tube, and the other to the focusing and accelerating anodes which project an electron beam against the fluorescent screen of the cathode ray tube, then my invention lends itself advantageously to the indication of phase relationship between these two sources of alternating current. v One application of my invention is illustrated in its use as part of a compass system. The particular details of the compass system, other than as brought out in the instant specification and as claimed herein, were invented by William A. Tolson, and disclosed in copending application Serial No.750,63l, led October 30, 1934. T'he utility of my invention, however. may well be illustrated in'connection with an earth inductor compass, and it will be seen from the ensuing disclosure that my invention has many other applications, Such as for radio beacons and for analyzing electric wave relationships in a variety of different circuits.

Accordingly, it is an object of my invention to provide an indicator of the cathode ray tube type in which a phase relationship between two existing alternating currents may be evidenced by the location of a light spot on the fluorescent screen of the cathode ray tube.y

Other objects and advantages of my invention include the provision of a device of the character mentioned in which the potentials for exciting the anodes are supplied directly from an amplifier which furnishes a voltage wave of desired amplitude, periodicity and wave form.

Still further objects and advantages oi my invention will become apparent upon reading the following detailed description in view of the accompanying drawing, in which the sole figure thereof represents diagrammatically one embodiment in association with an inductor compass system.

As is well known in the art, a cathode ray tube provides means for making an indication without involving the use of any rotating masses or other elements having appreciable inertia. The directive control of an electron beam within the cathode ray tube is usually accomplished by deflecting circuits which may be either of the magnetic or Ths invention relates New York, N. Y., a corporation of pair in the other of the circuits. The electrostatic plates may be disposed either within or externally of the envelope of the cathode ray tube.

Referring to the drawing, I show the cathode the usual cathode l, which may, if desired, be indirectly heated as by means of the filament 8. The control electrode 9 is not in all cases essential, but it has been shown for convenience in regulating the intensity of the light spot to be formed on the fluorescent screen through the action of the focused electron 9 is provided, it may be suitably biased as by means of a connection thereto from the potentiometer l0 disposed across the terminals of a battery Il or other source of potential. Connections are made, as shown, with the grounded cathode 1.

The peculiar manner of exciting the anodes of this cathode ray tube according to my invention may perhaps be best illustrated by its use in connection with an earth inductor compass. Such a compass may, for example, include a coil I2 which is rotated in the earths magnetic eld. The rotation may be produced as by means of a small synchronous motor I3, the power for which may be derived from any suitable alternating current source such as that shown at i4. This source may also be used, if desired, for exciting the deecting circuits which are herein represented by should be kept in synchronlsm (though it varies in phase) with respect to the alternating current generated by the coil I2. The phase variation results from any variable orientation of the field of the synchronous motor I3, such as produced when changing the course of the vessel on which the compass is carried. Furthermore, it is apparent that the coil I2 will generate one cycle of current during one revolution, and that during the same time the deecting circuits 2-2 and 3 3 will produce substantially one revolution of the magnetic eld for controlling the direction of the electron beam in the cathode ray tube.

' In order to provide a 90 phase displacement 2 between the current in coils .2 in reference to the current in coils 3, I introduce in the deiiecting circuits in the one case a suitable resistor I5 and in the other case a capacitor it. The resistive and capacitive values respectively are so chosen as to produce the desired 90 phase displacement. If a two-phase source of alternating current were available, it could, of course, be applied to the coils 2 and 3 in an obvious manner.

Because the synchronous motor it and the deflecting coils 2 and 3 are operated from a common source Hi, it will be clear that synchronism is automatically maintained between the deflecting circuits and the rotations of the inductor coil 5 l2. If the apparatus is carried on a moving vessel or on aircraft, then it is possible to malte use of the phase coordination between the coil l2 and the denecting circuits and thereby to indicate the direction in which the vessel or aircraft o may be headed.

The earths magnetism induces a small alternating current in the coil l2, the frequency of the current being dependent upon the speed of rotation of the coil. One complete revolution of the coil generates one complete cycle of alternating current. By means oi collector rings il and brushes le this current may be taken off and applied, say, across the grid and cathode leads of an amplifier tube i9. 'I'he grid 2@ may, if desired, be suitably biased by means of the battery 2l. Anode and screen grid potentials may be supplied from the source 22. The amplifier tube i9 may then be caused to function in the usual manner. More than one stage of amplification may be provided, if desired.

The intercoupling between stages may be either by means of transformers or by the usual form ci resistance coupling, as is well known in the art. In this instance I have illustrated a suitable network comprising the electron tubes lil, 23 and 31, each of which serves a. dierent purpose. The tube 23 normally draws very little current. One way of producing this result is to introduce between the cathode 2t and ground a high resistor 25, say, of the order of one megohm. This resistor is preferably shunted by a capacitor 2S permitting momentary currents of larger amplitude to how. 'I'he grid circuit includes a resistor 21 and is coupled by means of a capacitor 23 to the output circuit of the tube it.

The tube i9 provides substantially linear arnpliiication of a sine wave current. When a maximum Voltage is developed on the anode 3d a positive wave peak will then be applied across the capacitor 28 to the grid 29 which raises its potential just above the cut-oi point due to the fact that this grid is normally very negatively biased by the resistors 25 and 2l. A very sharply peaked-impulse is, therefore, transmitted by the tube 23, this impulse being developed into a space current of suitable amplitude (aided by the low impedance of the capacitor 26) for suddenly lowering the plate potential and biasing the grid 3l of the tube 31 below its cut-oil point.

Normally, the grid 3l may be so biased that a current of suitable amplitude will ow in the tube 3l, thereby developing a more or less saturated magnetic flux in the core of the transiormer ez. 1f the tube 31 becomes suddenly blocked, as

`when its grid momentarily goes negative, it will be seen that the stored energyin the transformer 32 must be dissipated through its secondary winding 33. It is possible in this manner to develop a very high potential such as is suitable for irnpress upon the anodes of a cathode ray tube.

As a means to this end I have indicated the secondary winding 33 having one terminal thereof connected to ground and thel other terminal connected to the accelerating anode 5. A lesser potential may be applied to the focusing anode l through a circuit which includes aftap @t on the potentiometer 35, the latter being disposed across the terminals of the secondary winding 3d.

In the operation of my invention the original sine waveI generated by the coil l2 is translated by the tube 23 into discrete impulses which may be made steep-sided and of very short duration. It is only when these impulses occur that voltages will be developed on the anodes or the cathode ray tube. Hence it is'possible to very sharply denne the position of a luminous spot to be displayed on the fluorescent screen t. While the deecting circuits 2 and 3 may be functioning continuously, there is no electron beam to be projected upon the screen t until impulses are impressed upon the anodes d and d. It is found, however, that the action of the focusing and aecelerating anodes brings the light spot to its position of maximum intensity somewhere along the arc of a circle. This circle is preferably concentric with the screen t and conveniently near the periphery thereof. The spot seems to develop gradually along an arcuate path starting from the edge of the screen. When the peak of the impulse passes, the spot fades out as it departs from the point of focus along another arcuate path toward the edge of the screen. The converging of these paths of approach and departure provides a desirable pattern for the image of the light spot, in that the point of convergence is very clearly defined. The angle subtended between the paths of approach and departure may be made quite sharp, if so desired, by merely providing suitable electrical constants in the design of the transformer 32.

A suitable scale 36 may be printed on the glass of the screen so as to provide reference markings for any desired indication, whether the device is used as a compass, as a radio beacon, or merely for indicating phase angles between two alternating currents.

In the embodiment of my invention as shown it is apparent that the directional eect of the earths magnetism produces an alternating current in the rotating coil l2 and the peaks of this current of one polarity are amplied and translated into voltage impulses of considerable niagnitude to be applied to the anodes of the cathode ray tube. The synchronous motor it is of that type wherein its armature makes one revolution during a single cycle of current from the source Hl. Since the mounting of the entire apparatus may be fixed in relation to the aircraft or vessel in which it is carried, and since the phase angle between the source of alternating current i and the alternating current generated in the coil i2 will vary with the orientation of the vessel, it is clear that the light spot appearing on the screen of the cathode ray tube will also 'be varied in its position on the circular scale. Ihus the direction in which the vessel is headed may be indicated.

Other applications of my invention will readily occur to those skilled in the art. Its use is by no means limited to a compass, since there is a considerable demand for an indicator having inprior art and by the spirit and scope of the pended claims.

I claim. as my invention: 1. In a device for indicating the phase angle between two wave trains of like frequency; a

means coupling said amplier and said thermi- .onic tube; a second amplifier whose output circuit includes an iron on said screen in accordance gie between the two trains.

2. In a device for indicating the phase angle between two alternating currents of like frequency; a cathode ray tube having deiiecting circuits, a focusing anode, and a iluorescent screen; means responsive to the action of one of said alternating currents and including said deflecting circuits for rotating the ray of said cathode path substantially concentric with said screen; a thermionic tube normally biased to cut-cil for amplifying the peaks of positive cycles lof the other of said alternating currents; an ampliiier tube whose output circuit includes an iron core transformer which is normally saturated by the currents normally iiowing in said output circuit; means including a coupling between said thermionic tube and said amplifier for suddenly dissipating said saturation effects to generate a high uni-directional potential; and a connection between said transformer and said focusing anode which applies a sole uni-directional potential for'focusing said cathode ray on said screen in accordance with the phase angle between the two currents.

3. In a device for indicating the phase angle between two alternating currents the combination of a cathode ray tube including deiiecting means, a focusing electrode, and a fluorescent screen; means for applying the rst of said alternating currents to said deiiecting means to thereby rotate said ray in a substantially circular path; and means including thermionic tubes for deriving positive impulses from the peaks of one phase of the second of said alternating currents and a saturation transformer across whose output terminals is established the sole anode potential to focus said ray on said tube to indicate the relative phase angle between said currents.

MILES A. McLENNAN. 

